55i Intelligence and Miscellaneous Articles. 



composed. The vapour which is disengaged yields, when condensed, 

 acicular crystals of caffeine : it is scarcely soluble in anhydrous alcohol, 

 even when heated; but a saturated boiling solution in alcohol of 95 de- 

 grees, yields on cooling prismatic crystals radiating from a common 

 centre ; it is more soluble in alcohol of 85 degrees, and the crystal- 

 lization is more abundant on cooling : the solubility always increases 

 with the proportion of water : pure water dissolves still more, and 

 a hot saturated solution becomes a mass on cooling. A cold solu- 

 tion, when slowly evaporated, gradually deposits a crown of very fine 

 crystals in mammillated groups. The aqueous solution while crystal- 

 lizing suffers more or less alteration by exposure to the air, and be- 

 comes yellow first, and afterwards greenish-brown. 



The crystals of this double salt, when slightly heated with hydrate 

 of potash, become of a vermilion or orange-red colour ; heated more 

 strongly, the mixture melts, becomes yellow, yields abundant ammo- 

 niacal vapours, and becomes brown, &c. When this double salt is 

 heated with concentrated sulphuric acid, an intense violet colour is 

 produced, and a bronze-coloured pellicle. Hydrochloric acid pro- 

 duces a similar but less marked effect ; nitric acid produces an orange- 

 yellow colour. 



When acetate of lead is added to the aqueous or alcoholic solution 

 of the double chlorogenate, a flocculent greenish-yellow precipitate 

 is formed : the trisacetate yields a pure yellow-coloured precipitate. 

 Nitrate of silver, alone, produces no effect ; but when previously mixed 

 with a very small quantity of ammonia, it produces a yellow colour 

 which becomes brown ; the liquid becomes turbid, and a pellicle of 

 reduced metallic silver floats upon it, and gradually extends over the 

 sides of the glass. 



Chlorogenic acid is obtained separately by treating chlorogenate 

 of lead with sulphuretted hydrogen ; the solution obtained, when 

 rapidly evaporated, yields a confused crystallization of chlorogenic 

 acid. 



This acid, when purified by small quantities of anhydrous alcohol, 

 is white, soluble in anhydrous alcohol, and more so in diluted al- 

 cohol ; it is very soluble in water and difficultly crystallizable. The 

 aqueous solution, when nearly saturated at a boiling heat, crystallizes 

 very slowly in microscopic crystals, radiating from a common 

 centre, and yielding in twenty or thirty days numerous spherical 

 agglomerations of y^yth to j g n th of an inch in diameter. 



The aqueous solution of chlorogenic acid has a very decided acid 

 reaction ; it reddens litmus strongly ; it is the active principle of the 

 various colours produced and described in the original salt of coffee. 

 When heated in a tube, it fuses, becomes of a yellow colour, boils 

 and leaves a thin and brilliant stratum of charcoal : its vapour con- 

 denses into a brown liquid, which, when rapidly heated, leaves a 

 very thin stratum of charcoal, which is iridescent. 



Ultimate analysis gave the following results : — 



Chlorogenic acid C14 H8 07. 



Carbon 56"0 



Hydrogen .. 5*6 



Oxygen 38*4 



100- 



